1. Field of the Invention
Many mechanisms require that a link be journaled for sliding and/or pivoting movement with respect to a support. One well-known device for this function is a bearing pin which extends perpendicularly from a support to permit movement in a plane perpendicular to the pin axis. Because of the importance of low production and assembly costs, bearing pins are often as simple as possible, usually have relatively loose tolerances, and are held in place by inexpensive techniques, such as staking. To minimize friction in the operating mechanism, it is common to provide a low friction surface layer or sleeve, such as a bronze bushing or a plastic sleeve or coating.
2. Description of the Prior Art
The assembly of known bearing pins having sleeves or bushings is usually a source of undesirable compromise, with either cost or performance suffering. This is particularly true if it is desired that the bearing pin incorporate retainer or axial thrust surfaces to keep the link from sliding axially off the bearing pin. Probably the oldest solution to this problem, for a pin having a thrust surface at the free end, is to provide some kind of head to retain the link directly, or to retain a thrust washer. If the pin is made of steel or similar low cost, high strength material, either a lot of material below the head is removed, as by a turning operation in a lathe; or a head is formed by upsetting, with risk of deformation of the pin surfaces underlying the bearing surface; or a still more expensive technique is required.
A frequent requirement is that the bearing sleeve or bushing not move with respect to the pin. This is especially the case where movement between the bushing and pin will cause looseness, or generate wear particles which damage or contaminate the apparatus in which the mechanism is used. When the bushing is made of a soft bearing metal, such as brass or a porous bronze, the bushing may simply be a press fit over the pin, in which the interference between the bushing and the pin itself provides a sufficient grip. Alternatively, and especially where the bushing includes a thrust surface at the end of the bearing pin adjoining the support to which it is fastened, the pin could be relieved slightly with respect to the end face of the bearing bushing, so that the bushing itself is held tightly against the support. However, if the bearing bushing is made of a low friction plastic (synthetic resin) material, a sufficient interference fit to guarantee that there be no relative movement may distort the somewhat elastic material of the bushing sufficiently that the bearing surfaces are no longer sufficiently true cylindrical or planar surfaces.